As a fastener element which is conventionally used for a slide fastener, a fastener element made of synthetic resin which are formed individually by injection-molding synthetic resin onto a fastener tape, a continuous fastener element which is formed by molding a mono-filament in a coiled shape or a zigzag shape, and a metallic fastener element which is formed by caulking an approximately Y-shaped metallic element material onto a fastener tape, and the like are known.
Further, in general, the fastener element made of synthetic resin is directly fixed to the fastener tape when injection molding. Therefore, by broadening a fixing area of the fastener element with respect to the fastener tape, fixing strength of the fastener element with respect to the fastener tape can be enhanced. For this reason, in a conventional fastener element made of synthetic resin, an element width dimension of each fastener element is set-large in order to ensure the fixing strength of the fastener element stably.
Whereas, since the metallic fastener element is attached to the fastener tape, for example by caulking an element which has an approximately-Y-shaped cross section, the metallic fastener element can easily obtain enough fixing strength without setting the element width dimension as large as in the fastener element made of synthetic resin as described above.
Generally, the fastener element, made of synthetic resin is molded so as to extend between a first surface, which becomes to be an outer surface of the fastener tape, and a second surface, which becomes to be a tape back face of the fastener tape, and the fastener element made of synthetic resin has a first half section which is disposed, on the first surface side of the fastener tape and a second half section which is disposed, on the second surface side of this fastener tape.
Further, such a fastener element made of synthetic resin is often avoided such that the first half section and the second half section have symmetrical shapes. However, for example, in order to enhance appearance quality (sense of beauty) of the fastener tape or in order to improve touch (texture) of the fastener element, the first half section and the second half section may be formed to be in a different and asymmetrical shape.
For example, WO 2010-082294 A (Patent Document 1) and Design Registration No. 1382201 (Patent Document 2) disclose fastener stringers in which the first half section of the fastener element has an appearance like a metallic fastener element.
For example, a fastener element 60 described in the Patent Document 1 is fixed to a tape side edge section of a fastener tape 65 by injection-molding thermoplastic resin, and as shown in FIGS. 18 and 19, a fastener element 60 comprises a first half section 61 disposed on a tape upper face side of the fastener tape 65 and a second half section 62 disposed on a tape lower face side and integrally formed with the first half section 61. Further, here, a vertical direction refers to a tape front and back direction which is orthogonal to a tape surface of the fastener tape 65. Also, a back and forth direction refers to a length direction of the fastener tape 65, and a horizontal direction refers to a tape width direction of the fastener tape 65.
In this fastener element 60, the first half section 61 includes a fixing section 61a which is fixed to the fastener tape 65, and an extending section 61b which extends from the fixing section 61a toward the outside of the tape. The extending section 61b has a tapering shape in which an element width dimension in the tape length direction gradually decreases toward a tip end section of the extending section 61b. 
In the first half section 61, in order to ensure the fixing strength with the fastener tape 65, the element width dimension in the lower end section (an end section on the side which is in contact with the fastener tape 65) of the fixing section 61a has a predetermined size.
Further, as shown in FIG. 19, the front side face and the back side face of the fixing section 61a in the first half section 61 is formed on a convex surface 63, which curves outwards in a convex shape such that the element width dimension of the first half section 61 gradually decreases from a tape surface of the fastener tape 65 toward an upper face of the fastener element 60. Accordingly, the first half section 61 is composed such that the element upper face, which is exposed to the outside directly, appears to be thin. Additionally, in the first half section 61, an interference avoidance section 61c, which inclines downward so as to gradually decrease a height dimension in the vertical direction of the fastener element 60 toward the tip end section of the extending section 61b, is formed.
The second half section 62 includes a body section 62a which is fixed to the fastener tape 65, a neck section 62b which extends from the body section 62a toward the outside of the tape and which is constricted so as to decrease the dimension in the element width direction, and a coupling head section 62c which extends further from the neck section 62b toward the outside of the tape. Therefore, each fastener element 60 in Patent Document 1 is coupled with a fastener element 60 of an engaging counterpart on the side of the second half section 62.
Since such a fastener element 60 in Patent Document 1 is composed of synthetic resin, it is light in weight compared to a metallic fastener element. Additionally, the fastener element 60 is formed so as to appear thinner than a conventional fastener element made of synthetic resin, while ensuring fixing strength with the fastener tape 65, so that the fastener element 60 has an appearance (show) like a metallic fastener element.
Therefore, a slide fastener, to which the fastener elements 60 in the Patent Document 1 are attached, looks stylish or adds a fashionable impression and at the same time is significantly reduced in weight, compared to a metal slide fastener and is formed.
Since the slide fastener, to which the fastener elements 60 in Patent Document 1 are attached, is provided with an interference avoidance section 61c as described above in each fastener element 60, for example in a case that the fastener elements 60, which is in a state that the left and right fastener elements 60 are coupled with each other, receives force in the tape front and back direction (push-up force) and a part of the slide fastener is bent in the direction in which the respective upper half sections of the elements are brought close to each other, it is possible to avoid interference between the first half section 61 of the fastener element 60 and the first half section 61 of a fastener element 60 on the side of an engaging counterpart.
Thus, even if the slide fastener receives push-up force, it is prevented to easily decouple the engagement between left and right fastener elements 60, and the coupled state can be stably maintained. Accordingly, in the slide fastener, it is possible to prevent causing so-called chain split in which engagement of fastener elements 60 are forcibly decoupled.
On the other hand, in Patent Document 2, a fastener chain, in which fastener elements having substantially the same shape as those in Patent Document 1 are attached to a fastener tape, is illustrated.
Additionally, for example, in Design Registration No. 1408991 (Patent Document 3), a fastener chain which design is further improved by providing more irregularities on an upper face of the fastener elements illustrated in Patent Document 2, is illustrated.